The present invention relates generally to high-frequency test technology. More particularly, the present invention relates to an apparatus and method for testing components built in circuit boards.
FIG. 1A is a schematic diagram of a conventional multi-layered circuit board 1 provided with a built-in capacitor 10 in a perspective view. FIG. 1B is a cross-sectional view of multi-layered circuit board 1 shown in FIG. 1A taken along a line II-II.
Referring to FIGS. 1A and 1B, multi-layered circuit board 1 includes a first dielectric layer 100, a second dielectric layer 102, and capacitor 10 built in circuit board 1. First dielectric layer 100 is formed over second dielectric layer 102. Built-in capacitor 10 includes a first electrode plate 104 and a second electrode plate 106. First electrode plate 104 in the example serves as a signal plate, and second electrode plate 106 serves as a ground plate. First electrode plate 104 is disposed between first and second dielectric layers 100 and 102, and second electrode plate 106 is disposed on a bottom surface (not numbered) of second dielectric layer 102. In other words, first electrode plate 104 and second electrode plate 106 are spaced apart by second dielectric layer 102. A signal pad 108 is formed at a top surface (not numbered) of circuit board 1, and more specifically, on the top of first dielectric layer 100 on which traces, active components, passive components or integrated circuits may be formed. Signal pad 108 is therefore a circuit node of a functional circuit (not shown) included in circuit board 1. Since capacitor 10 is built in circuit board 1, a via 110 is formed through first dielectric layer 100 to electrically connect signal pad 108 and first electrode plate 104. Via 110 is generally formed by forming an opening through first dielectric layer 100 by a mechanical drill or laser, and then filling in the opening with conductive material. First electrode plate 104 may include a lead 112 and a conductive pad 114 extending therefrom to electrically connect first electrode plate 104 and signal pad 108 through via 110.
During the formation of via 110, the opening may not be well formed such that an open-circuit issue may occur. For a multi-layered circuit board having built-in components, either passive or active, however, it may be difficult to test if there's an open-circuiting or short-circuiting in the circuit board. It is desirable to have an apparatus and method for testing a multi-layered circuit board provided with built-in components.